Method of preparing far-hydrolyzed cellulose esters



Aug. 24, 1943.

7 ACETYL c. 1.. ClANE 2,327,770

METHOD OF PREPARING FAR-HYDROLYZED CELLUOSE ESTERS Filed NOV. 23, 1940 FIG].

% ACETYL BY WEIGHT ACETONE FIGZ.

30 40 O 6O 7O 80 9o 7 BY WEIGHT ETHYL ALC'OHOL 7BY WEIGHT N'PROPYL ALCOHOL INVENTOR BY J ATTOR EYS Patented Aug. 24, 1943 Carlton L. Crane, 'Rocl1ester,N; .Y., assignor to Eastman Kodakflompanyflitochester, N. 31., a

corporation of New .llcrseyw,- 7

Amste am mediates 23, m dieiriaind266,856

7 15 Claims. (Cl. ace-'23s) This invention relates to the preparing oi iar hydrolyzed cellulose esters, in an aqueous solution of a water miscible organic solvent having a boiling point lower than that oiHwatenWhich solution contains a smallproport-ion of a 'mineral acid catalyst. j E

Heretofora in the preparing or far hydrolyzed cellulose esters, thecornpletedreaction mixture has been converted t 'oa hydr olyzingbathfior instance, by the-addition of aqueous organic acid theretofilf necessary, further water" or dilute acid was added from time totinie to promote the hydrolysis. In order to separate thefar 11ydrolyzed ester from Lthemas s; itwas necessary to employ large amounts of water, providing the ester had not been hydrolyzed to water solubility. Where water solubilitywasjattained, precipitation in volatile solvents in which the ester was insoluble has been employed. As the water is the lower boiling liquid in the mixture of acetic or some other'organic acid"andfwater,therecovery of the acetic acid or other 'acid' present was very much complicated. Q if 1 The presence 'ofa large quantity of lower iatty acid] in thef hydrolysis mass"; also makes "for a comparatively small rateofhydrolysi'sl of the. cellulose esters which, unless "considerable, care is employed, may result injdegrada't en of the cellulose ester.

One object of my invention is to provide method for far hydrolyzing'lower fatty acid esters of cellulose in which the liquid from which the ester is separated admits of easy recovery; Another object of my invention isto provide ahydrolyzing process which proceeds at a rate which retards degradation of the-cellulose ester being hydrolyzed. A,further object iof my invention is to provide a hydrolysisv process; which makes possible the easy separation o f the celle lose ester'irom the hydrolyzing liquid when the ester has been hydrolyzed to the desired acyl content. I have found that by starting withcellulose acetate or some other lower TELtlZYUaCidBSEBIIOf cellulose, which has, been prepared iand "purified in thegusual manner and: which: is then1redissolved in an aqueous solution'of awater miscible organic solvent having-aboiling point. lower than that of water .in which ,thercellulose ester; is so1-, uble, the, hydrolysis to water vvsusceptihilityior.

. Water solubility may be easilyic'arriediout by ing amineral acid catalyst andholdingeth'e tem perature .at room temperature or above butin most cases under the-boiling: point 20f. the .sol; vent. Insome cases-it is' desirableiito hold the reaction temperature above the boiling pointfo'f the liquid used as'a solvent inorder topromote solution. For instance, in theihydrolysis of cellulose acetateof .38-38.5'%]acetyl in alcohol-watermixtures boiling' temperatures are desirable. Where the starting material is-a cellulose ester containing dj drjgeamoum of acyl, it is ordin'ar1 ily necessary toadd additional water to the mass;

As the hydrolysisproceeds, the'vlater may be added with or'fwithout additional solvent. Itis preferred, however, to add the water without adclitional solvent, as I have found that this is more economical than by'adding'solvent with the water. w ,1 i a My invention relates to' the far hydrolyzing oi organic acid esters of cellulose, containing acyl groups ofZ-fi carbon atoms, in which the acetyl groups ,predominate. By the far hydrolysis of such a cellulose ester is meant reducing the acyl content tof water susceptibility or to water solubilityor in other WOI'dSlZO an acyl value between 28 and 13%. Ordinarily the cellulose esters,lhaving an acyl contentoi 13-19%, are water soluble while, those in the upper part of the range are susceptible tovpenetration by waiterand also are soluble in solvent mixturescontaining a considerable proportion of Water. i

As the starting material of my hydrolysis method a icjellulose ester is employed. One may use a fully. esterified cellulose ester providing :it is soluble in "the organic solvent which is employed. In the case of'the simple cellulose triacetaoe, however, no water miscible solventja having aboili'ng point less than that of water, is known. However, the ordinary commercial cellulose acetate, such as having an acetyl content of 38-42%, may be employed, the amount of water, in the initial dissolving liquid being adjusted tg the acyl content of the ester. With both the c ellulose acetate and other cellulose esters, such as cellulose acetate .propionate and cellulose acetate butyrate the amount of Water in the initial solvent used is governed by the acyl content of the starting material. For instance, if the starting material usedis a cellulose acetate, having an acetyl content of {l=1 .5-4 2%, or inpther words, nearthe beginning of acetone soluhility,,the dissolvingliquid, if acetone,,may not contain any water and after the esteris dissolved, the addition ofqwater will;;precipitate; it.

Therefore a small amountof ethyl or methyl al-.

cohol may bathe first addition ,to get the hy drolysisstarted'. .If, however, the starting material is a; cellulose acetate-having an acetyl content of approximately 38% ,the solvent usedto a k A f After the-dissolving of the cellulose. ester, a7

small amount of a mineral acid catalyst is added.

Hydrochloric acid is preferred for this purpose,

as'it gives a high rate ,of hydrolysis and results in products which are stable. Other mineral acidshowever, may be used if their properties are not objectionable. For instance, phosphoric acid can be employed, however,'the hydrolysis rate is considerably less than when hydrochloric acid is used. Nitric acid may be employed, however, there is a tendency to color the product.

With the use of sulfuric acid, the obtaining ofa stable product has to be considered. The proportion of catalyst employed is usually between .01% and 30%, based on the-cellulose ester. Any tem' perature which is at least room temperature may be employed. Ordinarily a temperature of 100 F. gives a satisfactory rate of. hydrolysis and, therefore, is suitable in this connection. As pointed out above, water is ordinarily employed as the hydrolyst in my hydrolyzing process, but alcohol may be used in whole or in part in this connection.

My process is economical in that the ester is dissolved originally, preferably in from 3-12 parts of 'the solvent or solvent mixture and besides the catalyst, additions of water are all that are re quired in carrying out my hydrolysis process.

Ordinarily, I prefer to use five parts of solvent or solvent mixture for each part of ester in 7 my process, but it is to be understood that this ratio may vary according to the solubility and viscosity' of the ester which is employed as the starting material. p Y

My invention contemplates the use of Water miscible solvents which will dissolve the cellulose esterinitially. This may be acetone or in the case of cellulose esters ,which have been bydrolyzed to a considerable extent, ethyl, propyl or methyl alcohol may be employed. For instance, with a cellulose acetate which has been hydrolyzed down to an acetyl content of 35%,

ethyl alcohol and water may be employed to dis-, solve the ester preparatory to its hydrolysis down to water susceptibility.

The attached drawing is a graph givingthe solubilities of cellulose acetates of varying degrees of hydrolysis in solvents which I have found useful. These graphs also point out the solubilities of cellulose acetate in the various mixtures of those solvents with water. Figure I shows the solubility of cellulose acetates of various acetyl contents in acetone-water mixtures. Figures II and III relate to the solubilities of cellulose acetates in ethyl alcohol-water and propyl alcohol-water respectively.

The solvent combinations for hydrolyzed mixed esters of cellulose depend upon several factors principally the proportion of the various acyls, the hydroxyl content and the viscosity. For example, a hydrolyzed cellulose acetate "propionateof 30-32% acetyl and -17% propionyl Will dissolve in mixtures of 85100% aqueous acetoneQ acetyl and A mixed ester with 25.'527.5% 15-17% propi0nyl will dissolve in' mixtures of YO-100% aqueous acetone. "A mixede'ster-with 23-25% acetyland 14.516.5% propionyl will dissolve in 66:1 7?) aqueous acetone I where the ester is water soluble, in which case only washing with the organic solvent can be employed. The organic solvent may easily be recovered from the mass. Having aboiling point below that of water, it may be distilled from the water, thus entailing a considerable saving in sol- .vent recovery cost. Also, if the cellulose ester is washed with the organic solvent, it is easily dried due tov the high vapor pressure of that solvent.

The

following examples illustrate my inventionz' Example I Seven pounds. of a cellulose acetate propionate,

having a propionyl content of 16% and an acetyl content of 31%, was dissolved in a mixture of '35; pounds of acetone and three pounds of water. i .7

pound of' acetone and .8 pound of hydrochloric acid (35%) wasadded thereto and the mass was kept at a temperature of 10091 for 36 hours. Ten pounds of water was added thereto and after 36 more hours, 15 pounds ofwater'was added and after'36 further hours, 15 more pounds of water was added. The hydrolysis was allowed to go for 189hours whereupon itwas precipitated and Washed in Water.. Acellulose ester was ob tained having an acetyl content of 13.9% and-a propionyl content of 10.4%.

' Example II A mixture of .3 pound of water, 155 grams of hydrochloric acid (35%) and one pound of acetone was added thereto. The mass" was then maintained'at F. for 72 hours. At the'fol-l lowing times, the designated amounts of'water. Were addedtothemass: 1

Hours sue:

The resulting Water-susceptible cellulose acetate lulose. acetate" form'ed wasflprecipitated and 1 I washed with water. A cellulose e'ster 'was' i ob"- tained havingan acetylqcon'tento'f '31.9%.; If. desired, instead of precipitatingat this point, further additions' of wat'er may be made and Three pounds of a cellulose acetate, having an,

ethyl alcohol and water at 260 F,

the hydrolysis may be carried out to a pointat which the acetyl content isbetweenlB and 19% to obtain a water solubleester. Thiswould necessitate-precipitating with acetone or with, al-

cohol. v i g i Example IV 1 pounds of cellulose acetate, having an acetyl content of 321 33 was dissolved in nine pounds of a mixture of equal parts of 95% ethyl alcohol and water at 150 F. cc. of 95% sulfuric acid dissolved in one pound of ami x' ture of equal parts of 95% ethyl alcohol and water was added to the solution. The mass was divided into two equal parts, one part being al.' lowed to hydrolyze hours andthe other '48 hours. The fifteen-hour hydrolyzed ester was precipitated-in water, washed and dried. "Ifhe forty-eight-hour hydrolyzed cellulose acetat was precipitated in methyl alcohol, washed in methyl alcohol and dried. The solubilityand acetyl content were as follows:

Time ol 1 acetonez4 water H2O I Aectyl Per cent 27. 6

48 hrs Swollen Example V such armixture is about. 180? However, the hydrolysisflwas carried outzat p? F. or. 20 F. above the boiling pointof the mixture in order to promotesolution of the cellulose. ester therein.

l r't a l a c m an i sv he x m plus (-1-) indicates-solubility and a minus (4-) designates insolubility.

I im: ,m llAprocess fonpreparing-xa far-hydrolyzed cellulose ester which comprises dissolving a low.-

, or fatty acidesterof cellulosein a solvent therecellulose :ester: which, comprises dissolving a cellulosesacetate iri. a. solvent therefor comprising an organic solvent which is water-miscible and v has a boiling point less than that of water, addsolved in nine pounds of n-propyl alcohol; at

159 F. 5 cc. of sulfuric acid (95%) dissolved in one pound of 40%n-propyl alcohol was added to the solution, The mass was dividedinto two parts, the first half being hydrolyzed 15 hours and the second half being hydrolyzed 48 hours. The first half was precipitated, washed 'infwater and dried, the second half was precipitated; washed in methanol and dried. The sclubilities and acetyl contents were as follows:

Time of .1 ae'etonezl water F a i0, Acetyl,

Per cent 26. 1 I 16. a

15 hrs 48 hrs Swollen Example VI separated into two equal parts, one-half being i allowed to hydrolyze for nine hours and the other half for 15 hours. In both cases the ester was precipitated, washed in water and dried. The solubilities and acety1 contents were as follows:

Time of hydrolysis l acetone: 4 water 1 acetone: 1 water 4 acetone:

1 water Acotyl Per cent 9 hrs 31.1 15 hrs Swollen Insol. Sol. Insol. 29. 2

It will be noted that the actual percent composition of the solvent mixture here is 47.5% ethyl alcohol by weight. The boiling point of ing a mineral acid hydrolyzing catalyst and a compatible hydrolyst thereto and maintainin at, at least, room temperature but below the boiling point of the solvent, accompanied by additions of. water from time to. timeto keep" the cellulose acetate in solution until it has an acetyl content between 28% and 13%.

i 3. A process i for preparing .a far-hydrolyzed cellulose ester which comprises dissolving alower fatty acidesterof cellulose in a solvent therefor"comprising an organic solventw'nich is water-miscible and has a boiling point less than that ofawater adding a mineral acid hydrolyzingzeatalystand water. inva. compatible amount thereto, and maintaining at, at'least, room teme perature but below the-boiling point. of thelsolvent, accompanied-byadditions of water from time vto ,time to. keep the cellulose ester in so-Z lution-untihthe cellulose ester has an acyl eontent between 28% and13%. 4. A process for preparing a far-hydrolyzed cellulose ester' which comprises dissolving a lower fatty acid ester of cellulosein a solventltherefor comprising acetone, adding a mineral acid hydrolyzing catalyst and a compatible amount of water thereto and maintaining at, at least, room temperature but below ,the boiling point of the solvent, accompanied by additions of water from time to time to keep the cellulose ester in solution until the cellulose ester has an acyl conf tact between 28% and 13%.

5. A process for preparing a far-hydrolyzed cellulose ester which comprises dissolving a lower fatty acid ester of cellulose in a solvent therefor comprising an organic solvent which is watermiscible and has aboiling point less than that of water, adding a hydrochloric acid hydrolyzing catalyst and a compatible hydrolyst thereto and maintaining at, at least, room temperature but below the boiling point of the solvent, accompanied by additions of water from time to time to keep the cellulose ester in solution until the cellulose ester has an acyl content between 28% and 13%.

, 6. A process for preparing a far-hydrolyzed cellulose ester which comprises dissolving a lower fatty acid ester of cellulose in a solvent therefor comprising an organic solvent which is watermiseible and has a boiling point less than that 4 ri va ra df m fa i i i i echnicians fi -i alyst and a compatible hydrolystfthr'eto and maintaining at atemperatureof '1Q0"Fl, acconi-f s pani'ed by'addit'ionsof water from timetotiine to kee'p'the' cellulose {ester'in solution untilthe cellulose ester has anacyl content between 28% and13%. '7. A process for preparing a far-hydrolyzed cellulose ester whichtcomp'r'isesjdissolving a lower fattyacid'ester of" cellulose a solvent therefor comprising an organic 'solvent which is watermis'cible and has a boiling point less than that of water, adding a hydrochloric acid hydrolyzing catalyst and-water in'a compatible amount and maintaining at at least roomtemperature but below the boiling point of the solvent, accompanied by additions ofwat'er from" time to time to keep the cellulose in solution until the cellulose ester has an acyl content between'28% and 13%, 8.-A process for preparing a far-hydrolyzed cellulose ester which comprising dissolving a cellulose acetate in a solvent therefor comprising acetone; adding a hydrochloricacid hydrolyzing catalyst and water in compatible amount and maintaining atapproximately 100 F., accompanied by additions of water from time to time to keep the cellulose ester 'insolution until the cellulose ester has an-acyl contact between 28% and13%. m r

9. A process for "preparing a *farhydrolyzed cellulose ester which comprises treating a lower fatty acid ester of cellulose, having an acyl content of approximately 38.5% to approximately 32%, with aqueous alcohol the alcohol having a boiling point less than that'of water and approximately 1-5% of a mineral acid hydrolyzing catalyst at a temperature conducive to dissolving of thecellulose estertherein until the cellulose esterhas an acyl content between 28vand 13%. 10. A process for preparing a far-hydrolyzed cellulose acetate which comprises treating a cellulose acetate, having an acetyl content of approximately 38.5% to approximately 32%, with aqueousalcohol the alcohol having a boiling point less than thatfof water 'andapproximately 1-5% of a mineral acid hydrolyzing catalyst at a temperature conducive to ,dissolvingof the celluloseester therein-until the cellulose ester has an acetyl content between 28-and 13%.

v content between 28 and 13%.

conducive to dissolving -of; the cellulose .ester therein-until the cellulose. ester has anacyl-content-between 28 and. -13%,. V

-12. A processfor prepar inga-far l iyolrolyz edv cellulose acetate which comprises treating a cel lulose acetate having-an acetyl content of approximately 33 withaqueous alcoholthe alcoholhavingaboiling point less than that of watei and approximately 1-5%' of a 'mineral acidfhy drolyzing catalyst at a temperature conducive to dissolving of the cellulose ester therein until the, cellulose ester has an acetyl contentbetween 28 13% 4 13. -A process for cellulose ester which comprises treating. a lower fatty acid ester of cellulose, having an acyl content between approximately 38.5% and approxi mately 32%, with aqueous'ethyl alcohol and approximately 1-5% .of hydrochloric acid at a temperature conducive to dissolving of the cellulose ester therein until the cellulose ester has an acyl 14. A process for preparing a far-hydrolyzed cellulose ester which comprises treating a lower fattyacid esterhof cellulose having anacylcontent between approximately 38.5% and approximately 32% with aqueous ,ethylfalcoholand" ap-i proximately 1 5% of a mineral acid hydrolyzin'g catalyst at a temperature conducive tov dissolve ing of thecellulose esterjtherein untilthe cellu; lose ester has anlacyl content 'between '28 and 15. A process for preparing afar-hydrolyzed cellulose .ester which comprises treating a lower fatty acid ester of cellulose having an acylcotir. tent between approximately 38.5% f anda proxi; mately 32% with aqueous ethyl alcohol and a'p proximatelyl5% of sulfuric acid at a temper ature conducive to dissolving of the cellulose ester therein until the cellulose ester has an acyl content between 28 and 13%.

CARLTON L. CRANEI" r pa a" 'f s-hirdr l d l 

